unmanaged: true - Does not ignore file marked for being 'unmanaged'

When adding `unmanaged: true` to the `.sync.yml` the file and running `pdk convert` the file is not ignored.

Steps to reproduce
--------------------------
1) Ensure '.travis.yml' file exists within the module root directory
2) Populate the `.sync.yml` file with .travis.yml: unmanaged: true (At the bottom I have included the specific `.sync.yml` file I have used
3) Run `pdk convert' (with flag N)
4) Confirm module has not been converted
5) Inspect the convert_report.txt file
6) Confirm the report shows intended changes for `.travis.yml` file
7) Actually run the convert this time: `pdk convert` (with flag Y)
8) Confirm there has been changes made to `.travis.yml`.

Expected Results
-----------------------
I would expect the .travis.yml file to be ignored and no changes to be pushed to the file from the template.

Actual Results
---------------------
The file marked for being unmanaged is still managed via the template. When wanting to ignore .travis.yml the changes are still pushed out to the file.

Example of .sync.yml I was used (for netdev_stdlib module):

---

.travis.yml:

  unmanaged: true

The output convert_report.txt has been attached.